Fish deaths

[Christopher D Kaufman]

Dear fellow fishpeople,

We are having a problem with our fish stocks. Over this past weekend, 
three tanks had ~50% mortality. The fish exhibited a tendency to float, 
and had to exert much energy in order to swim downwards. This progressed 
to them swelling up, their eyes bulging out and eventually their 
abdomens bursting open and the fish perishing. We think this may be from 
uncontrolled swelling of the swim bladder, or possibly a blockage of their 
intestines. We also think these events occur (it has happened before) 
following a radical weather change. This time it followed a sudden plunge 
in temperature (30's to several degrees below zero). This may be affecting 
the local water supply in a way that can't be rectified by our filtration 
system, ie: pH, osmolality (from road salt washing into the reservoir?).
We're contacting our local water supplier to ask them about these 
possibilities. 

So my questions are: has anyone else witnessed these symptoms in their fish 
stock? Does anyone have any ideas what is causing this and how to 
treat/prevent it? Does anyone know how pressure is regulated in the 
zebrafish swimbladder, like ion or solute concentration?

Any help you can give would be greatly appreciated.
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Chris Kaufman                     |  This space for rent |    
kaufman at molbio.cbs.umn.edu        | Inquire within       |
University of Minnesota           ------------------------
Molecular, Cellular and Developmental Biology and Genetics
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